Extreme Detonation under Odd Circumstances

[LiamPSD]

Hi all, I need some input from different directions.

I have built a few supercharged (1bar MAP) engines running 9:1 comp ratio, now on these engines one has got a normall head, no porting etc etc, and on the second engine it has a worked head, ported, using bigger exhaust valves.

They both use cold plugs (bosch grade 4 platinums)and both use a stock cam, which is more than up to the job. water/oil temps on both engines are 70-90 degs/ 95-105 degs average.

the first engine (std head) runs like a dream goes like it should and couldn't be better.
Now the second engine had all sorts of detonation porblems, it pinks on initial pick up at WOT ( AFR 13.0-14.5:1) and then pulls out of it, then pulls back in again at the top end of the rev range. during this time the AFR is around 12.5-13:1 In my mind the AFR seems to be ok.
There are no signs of pinking/detonation on the spark plugs they all look healthy, but upon removal of the head there was a different sight. Around the exhaust valve (combustion wall side) there is severe pitting on the head and the edge of the piston but there is no pitting on the exhaust valve or the seat no signs what so ever.
Now I think this could be due to severe heat build up of the exhaust gases and not enough scavenge on the cylinder.
The reasoning behind my statement is due to the fact that the worst case is on piston #3 and least effected is #1 and where the manifold collects ( stock cast iron) the largest ammount of material is around #3.
I can provide pics if needed but what do you guys think to this, I am a bit confused.
thanks in advance,
Liam.

 

[IRstuff]

Seems like this is more of an Automotive Engine and Fuel Engineering forum71 question.

TTFN

 

[O320]

Send us some pictures!

 

[dantonks]

liam

i would agree that you may not have enough exhaust scavengeing on that cylinder.

also what does the water gallerys look like around cyl no3 ( are you getting enough coolant flow in that area?)


Cheers

Dan

 

[SMOKEY44211]

Here's my 2 cents. Ported head flows better. Better cylinder filling. Higher volume of air produces higher cylinder pressure and temp. bringing it over the detonation threshold. If I had a way to bet on it and collect that's where my money is.-------Phil

 

[LiamPSD]

HI guys sorry I havn;t taken any pics as of yet I have been a little busy to work on it.
But I have been thinking, There is a combination of everything causing this dettonation, But I think it can be cured by sorting out cam timing increasing duration, acceleration and lobe seperation angles. I will gives this a go with and see what happens.
I will also post pics when I get the chance.

Liam

 

[crysta1c1ear]

I agree with SMOKEY44211
By supercharging the engines, you seem to be heading towards the limits and the engine that gets there first is the one with the better airflow and hence more stuff inside. It would have surprised me if it WASN'T the second engine with a worked head, ported, and using bigger exhaust valves, that had the problems.

You say the air fuel ratio is okay, but okay for what? For CO emissions, NOx emissions, for loads of power?

"Fuel in for coolin'?"